TLR9 activation in large wound induces tissue repair and hair follicle regeneration via gamma delta T cells

The mechanisms underlying tissue repair in response to damage have been one of main subjects of investigation. In this study, we leveraged the wound-induced hair neogenesis (WIHN) models in adult mice to explore the inner correlation. Our investigation revealed that heightened release of mitochondrial DNA (mtDNA) accompanying tissue damage activated the toll-like receptor 9 (TLR9) pathway, influencing the repair process and the ultimate number of regenerated hair follicles. Furthermore, our analysis of single-cell RNA sequencing comparisons demonstrated increased TLR9 activation was associated with the recruitment of gamma delta T cells ({gamma}{delta}T). Inhibition of {gamma}{delta}T cell recruitment led to a reduction in the population of {gamma}{delta}T cells and a more fibrotic healing outcome. Notably, these {gamma}{delta}T cells exhibited distinctive high production of AREG, contributing to the rapid increase of local AREG levels around the epidermis and influencing the fate commitment of keratinocytes. These findings provide new insights into the roles of TLRs as critical mediators in the sense of tissue damage, the modulation of immune cell activity, and the ultimate influence on healing outcomes. TeaserStarting with how tissue injury stimulates downstream tissue repair and regeneration through relevant signals, this study explored the phenomenon and correlation between tissue damage and TLR9, and the effect of TLR9 on {gamma}{delta}T, keratinocytes and the healing outcomes.